Cyanine Dyes

ABSTRACT

The object of the present invention is to provide organic dye compounds which exert satisfactory optical absorption properties and thermal resistance when used in high density optical recording media. The above object is solved by specific trimethine cyanine dyes, light absorbents and optical recording media which comprise the cyanine dyes, and preparations for the cyanine dyes comprising either reacting a benzoindolium compound having a compatible leaving group with a pyrazinoimidazolium compound having a reactive methyl group; or reacting a benzoindolium compound having a reactive methyl group with a pyrazinoimidazolium compound having a compatible leaving group.

TECHNICAL FIELD

[0001] The present invention relates to novel organic dye compounds,particularly, to trimethine cyanine dyes which are useful in highdensity optical recording media.

BACKGROUND ART

[0002] In a multimedia age, optical recording media such as a compactdisc recordable (CD-R, a write-once memory using compact disc); and adigital versatile disc (DVD-R, a write-once memory using digital videodisc), are now of great importance. Optical recording media can beclassified roughly into inorganic optical recording media which haverecording layers composed of inorganic substances such as tellurium,selenium, rhodium, carbon, or carbon sulfide; and organic opticalrecording media which have recording layers composed of light absorbentsthat are mainly composed of organic dye compounds.

[0003] Among these optical recording media, organic optical recordingmedia are usually prepared by dissolving a polymethine cyanine dye in anorganic solvent such as 2,2,3,3-tetrafluoro-1-propanol (abbreviated as“TFP” hereinafter), coating the solution onto the surface of apolycarbonate substrate, drying the solution to form a recording layer,and sequentially attaching closely a reflection layer made of a metalsuch as gold, silver or copper and a protective layer made of anultraviolet ray hardening resin onto the surface of the recording layer.When compared with inorganic optical recording media, organic ones havethe drawback that their recording layers may be easily changed byexposure to light such as reading and natural light, but have theadvantage that they can be manufactured at a lower cost because theirrecording layers can be formed by preparing solutions of lightabsorbents and directly coating the solutions onto the surface ofsubstrates. Also, organic optical recording media are now becoming thepredominant low cost optical recording media because of the advantagesthat they are mainly composed of organic substances so that they aresubstantially free of corrosion even when contacted with moisture or seawater; and because information, which is stored in optical recordingmedia in a prescribed format, can be read out using commercializedread-only players using thermal-deformation-type optical recordingmedia, a kind of organic optical recording media.

[0004] What is urgently required of organic optical recording media isto increase their recording capacity to suit this multimedia age. Theresearch for such an increment now eagerly continued in this field is toshorten the wavelength of 775-795 nm now used as a writing light to thewavelength of 700 nm or less. However, most of the polymethine cyaninedyes, which had been explored for CD-Rs, could not suitably read andwrite information using laser beams with wavelengths of 700 nm or less,and therefore they could not fulfill the need for high storage densityrequired in many fields.

[0005] There exists a problem of the thermal decomposition of dyes asanother causative of hindering the high storage density in organicoptical recording media. In organic optical recording media, pits areformed by using the heat, generated when dyes absorb laser beams, to bemelted and decomposed, however, most of conventional polymethine cyaninedyes have relatively high decomposition points independently apart fromtheir melting points, and the temperature difference between the meltingpoints and decomposition points; and thus, the formation of pits becomesrough when irradiated with laser beams, and the decomposition heatconducts to around the irradiated points and deforms the already formedadjacent pits, resulting in a difficulty of stably forming minute pitson restricted sites at a relatively high density.

[0006] In view of the foregoing, the object of the present invention isto provide organic dye compounds having satisfactory properties in lightabsorption and thermal resistance.

SUMMARY OF THE INVENTION

[0007] To attain the above object, the present inventors eagerly studiedand screened compounds and found that specific trimethine cyanine dyes(hereinafter may be abbreviated as “cyanine dyes”), which are obtainablethrough a step of reacting a benzoindolium compound having a compatibleleaving group with a pyrazinoimidazolium compound having an activemethyl group; or reacting a benzoindolium compound having an activemethyl group with a pyrazinoimidazolium compound having a compatibleleaving group, have absorption maxima in a visible region andsubstantially absorb visible light with wavelengths around 650 nm whenin a thin layer form, and have a relatively high decomposition pointsand thermal resistance. The present inventors also confirmed that thesecyanine dyes stably form minute pits on the recording layers at arelatively high density when used in optical recording media andirradiated with laser beams with wavelengths around 650 nm. The presentinvention was made based on the creation of the novel organic dyecompounds and the discovery of their industrially usefulcharacteristics.

BRIEF EXPLANATION OF THE ACCOMPANYING DRAWINGS

[0008]FIG. 1 shows the visible absorption spectra of one of the cyaninedyes of the present invention when in a solution form and in a thinlayer form.

[0009]FIG. 2 shows the visible absorption spectra of another cyanine dyeof the present invention when in a solution form and in a thin layerform.

[0010]FIG. 3 shows the results of the DTA and TGA of one of the cyaninedyes of the present invention.

[0011]FIG. 4 shows the results of the DTA and TGA of another cyaninedyes of the present invention.

BEST MODE OF THE INVENTION

[0012] The present invention solves the above object by providing thecyanine dyes represented by the Formula 1.

[0013] In Formula 1, R₁, R₂ and R₃ are the same or different aliphatichydrocarbon groups, for example, those which usually have up to eightcarbon atoms such as methyl, ethyl, propyl, isopropyl, 1-propenyl,2-propenyl(allyl), isopropenyl, butyl, isobutyl, sec-butyl, tert-butyl,2-butenyl, 1,3-butadienyl, pentyl, isopentyl, neopentyl, tert-pentyl,1-methylpentyl, 2-methylpentyl, 2-pentenyl, hexyl, isohexyl,5-methylhexyl, heptyl, and octyl groups, which may have one or moresubstituents, for example, halogens such as fluorine, chlorine, bromine,and iodine; ether groups such as methoxy, trifluoromethoxy, ethoxy,propoxy, isopropoxy, butoxy, tert-butoxy, phenoxy, benzyloxy, andnaphthoxy groups; ester groups such as methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, acetoxy, trifluoroacetoxy, and benzoyloxy groups;aromatic hydrocarbon groups such as phenyl, trifluoromethoxy, o-tolyl,m-tolyl, p-tolyl, xylyl, mesityl, naphthyl, o-cumenyl, m-cumenyl, andp-cumenyl groups; heterocyclic groups such as pyridyl, furyl, thienyl,and pyranyl groups; and other groups such as hydroxy, carboxy, nitro,and cyano groups.

[0014] In Formula 1, Z₁ and Z₂ each represents a condensed naphthalenering or a condensed quinoxaline ring for forming a benzoindolenine ringand a pyrazinoimidazole ring, respectively. Either or both of thecondensed naphthalene ring and the condensed quinoxaline ring may haveone or more substituents including aliphatic hydrocarbons andhalogen-substituted aliphatic hydrocarbons such as methyl,trifluoromethyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,and tert-butyl groups; halogens such as fluorine, chlorine, bromine, andiodine; ether groups such as methoxy, trifluoromethoxy, ethoxy, propoxy,isopropoxy, butoxy, and tert-butoxy groups; ester groups such asmethoxycarbonyl, trifluoromethoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, phenoxycarbonyl, acetoxy, trifluoroacetoxy, andbenzoyloxy groups; amino groups such as methyl amino, dimethyl amino,ethyl amino, diethyl amino, piperidino, anilino, o-toluidino,m-toluidino, and p-toluidino groups; amido groups such as acetamide andbenzamide groups; and others such as hydroxy, carbonyl, nitro, and cyanogroups.

[0015] In Formula 1, X⁻ represents a counter ion. Although the counterion is not specifically restricted and varied depending on use, it canbe appropriately selected in view of the solubility of the cyanine dyesin each organic solvent used and the stability of the dyes in a glassstate. Examples of such are fluoric acid, chloric acid, bromic acid,iodic acid, phosphoric acid, perchloric acid, periodic acid, phosphoricacid hexafluoride, antimony acid hexafluoride, tin acid hexafluoride,fluoroboric acid, and tetrafluoroborate ions; organic acid anions suchas thiocyanic acid, benzenesulfonic acid, naphthalenesulfonic acid,p-toluenesulfonic acid, benzenecarboxylic acid, alkylcarboxylic acid,trihaloalkylsulfonic acid, alkylsulfonic acid, trihaloalkylsulfonicacid, and nicotinic acid ions; and metal complex anions such as those ofazo, bisphenyldithiol, thiocatecholchelate, thiobisphenolatechelate,bisdiol-á-diketone, and their related compounds. In the cyanine dyesrepresented by Formula 1, structurally different cis/trans isomersthereof, if exist, are all included in the present invention.

[0016] Concrete examples of the cyanine dyes of the present inventionare those which are represented by Formulae 1 to 27 having the followingcharacteristic features that they have absorption maxima in a visibleregion, substantially absorb visible light with wavelengths around 650nm when in a thin layer form, and have a relatively high decompositionpoint and thermal resistance. Thus, the above cyanine dyes can beadvantageously used as light absorbents in optical recording media whichuse laser beams with wavelengths of around 650 nm when in a thin layerform, particularly, in high density optical recording media such asDVD-Rs which use laser beams with wavelengths of 635-660 nm as a writinglight.

[0017] The cyanine dyes of the present invention can be prepared byvarious methods. When the production cost is weighed, the cyanine dyescan be preferably prepared through a step of either reacting abenzoindolium compound having a compatible leaving group with apyrazinoimidazolium compound having a reactive methyl group; or reactinga benzoindolium compound having a reactive methyl group with apyrazinoimidazolium compound having a compatible leaving group.According to this method, the cyanine dyes of the present invention canbe produced in a satisfactorily high yield by either reacting thecompounds, represented by Formula 2 having R₁ and Z₁ corresponding toFormula 1, with the compounds represented by Formula 3 having R₂, R₃ andZ₂ corresponding to Formula 1; or reacting the compounds, represented byFormula 4 having R₁ and Z₁ corresponding to Formula 1, with thecompounds represented by Formula 5 having R₂, R₃ and Z₂ corresponding toFormula 1. Formula 2:

[0018] For example, adequate amounts (usually, about equimolar) of thecompounds represented by Formulae 2 and 3 or the compounds representedby Formulae 4 and 5 are dissolved in an appropriate solvent and reactedat ambient temperature or at a higher temperature under heating andstirring conditions, for example, by heat refluxing, optionally afteradmixed with an adequate amount of a basic compound(s) such as sodiumhydroxide, potassium hydroxide, sodium acetate, potassium acetate,sodium carbonate, potassium carbonate, calcium carbonate, sodiumbicarbonate, potassium bicarbonate, ammonia, triethylamine,N,N-dimethylaniline, N,N-diethylaniline, N-dimethyl pyrrolidone,piperidine, morpholine, pyridine, and1,8-diazabicyclo[5.4.0]-7-undecene; an acid compound(s) such ashydrochloric acid, sulfuric acid, nitric acid, methane sulfonic acid,p-toluenesulfonic acid, acetic acid, anhydrous acetic acid, anhydrouspropionic acid, trifluoroacetic acid, and trifluorosulfonic acid; or aLewis acid compound(s) such as aluminum chloride, zinc chloride, tintetrachloride, and titanium tetrachloride.

[0019] Examples of the solvents used in the present invention includehydrocarbons such as pentane, hexane, cyclohexane, octane, benzene,toluene, and xylene; halogen compounds such as carbon tetrachloride,chloroform, 1,2-dichloroethane, 1,2-dibromoethane, trichloroethylene,tetrachloroethylene, chlorobenzene, bromobenzene, and α-dichlorobenzene;alcohols and phenols such as methanol, ethanol, 1-propanol, 2-propanol,1-butanol, 2-butanol, isobutyl alcohol, isopentyl alcohol, cyclohexanol,ethylene glycol, propylene glycol, 2-methoxyethanol, 2-ethoxyethanol,phenol, benzyl alcohol, cresol, diethylene glycol, triethylene glycol,and glycerine; ethers such as diethyl ether, diisopropyl ether,tetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole,1,2-dimethoxyethane, diethylene glycol dimethyl ether,dicyclohexyl-18-crown-6, methyl carbitol, ethylcarbitol, methylcellosolve, and ethyl cellosolve; ketones such as furfural, acetone,ethyl methyl ketone, and cyclohexanone; acids and derivatives thereofsuch as acetic acid, anhydrous acetic acid, anhydrous propionic acid,trichloroacetic acid, trifluoroacetic acid, anhydrous propionic acid,ethyl acetate, butyl carbonate, ethylene carbonate, propylene carbonate,formamide, N-methyl formamide, N,N-dimethylformamide,N-methylpyrrolidone, N-methylacetamide, N,N-dimethylacetamide,hexamethylphosphoric triamide, and trimethyl phosphate; nitrites such asacetonitrile, propionitrile, succinonitrile, and benzonitrile; nitrocompounds such as nitromethane and nitrobenzene; sulfur atom-containingcompounds such as dimethylsulfoxide and sulfolane; and water, which allcan be used in an appropriate combination, if necessary.

[0020] In the case of using the above solvents, the greater the volumeof solvents the lower the reaction efficiency becomes. On the contrary,the lower the volume of solvents, the more difficult the homogenousheating and stirring become, and the more undesirable side-reactions mayeasily occur. Thus, the solvents should preferably be used in an amountup to 100 times by weight of the material reactants used, usually, it ispreferably used in the range of 5-50 times. Depending on the types ofthe material compounds and the reaction conditions used, the reactionshould preferably be terminated within 10 hours, usually, within 0.5-5hours. The reaction procedure can be monitored by conventional methodssuch as thin layer chromatography, gas chromatography, andhigh-performance liquid chromatography. After completion of thereaction, the intact reaction mixtures, if necessary, can be subjectedto conventional counter-ion exchange reaction to obtain the cyanine dyesof the present invention having a desired counter ion. All the cyaninedyes represented by Formulae 1 to 27 can be easily obtained in a desiredyield by the above methods. The benzoindolium compounds and thepyrazinoimidazolium compounds represented by Formulae 2 to 5 can beobtained by the method disclosed in Japanese Patent Kokai No. 316,655/98applied for by the same applicant as the present invention or inaccordance therewith. In Formulae 2 to 5, X₁ ⁻ and X₂ ⁻ are the same ordifferent counter ions as those in Formula 1. L is a compatible leavinggroup and is usually selected from monovalent aniline groups such asanilino, p-toluidino, p-methoxyanilino, p-ethoxycarbonylanilino, andN-acetylanilino, and derivatives thereof.

[0021] The cyanine dyes thus obtained can be used in the form of anintact reaction mixture for some uses, however, prior to use, they arepurified by conventional methods used for purifying the relatedcompounds such as dissolution, extraction, separation, decantation,filtration, concentration, thin layer chromatography, columnchromatography, gas chromatography, high-performance liquidchromatography, distillation, crystallization, and sublimation. Ifnecessary, these methods can be used in an appropriate combination. Foruse as light absorbents in high density optical recording media such asDVD-Rs and dye lasers, the cyanine dyes of the present invention shouldpreferably be purified by the methods such as distillation,crystallization and/or sublimation, prior to use.

[0022] Now explaining the uses of the cyanine dyes of the presentinvention, as already described above, the cyanine dyes have absorptionmaxima in a visible region, substantially absorb visible light withwavelengths around 650 nm when in a thin layer form, and have arelatively high decomposition point and thermal resistance. In addition,most of the cyanine dyes have only decomposition points, i.e.,temperatures at which the cyanine dyes used as testing samples start toreduce their weights when determined on the later describedthermogravimetric analysis, undistinguishable from their melting points,i.e., the temperatures at which the cyanine dyes as testing samplesstart to absorb heat when determined on the later described differentialthermal analysis, where the temperature difference between a meltingpoint and a decomposition point is within 10° C.; and promptly decomposeat around their decomposition points. Thus, the cyanine dyes of thepresent invention have a variety of uses in the fields of opticalrecording media, photochemical polymerization, solar batteries, dyeing,etc., which require the organic dye compounds having such a relativelyhigh decomposition point and thermal resistance. Particularly, thecyanine dyes of the present invention having the above properties can beadvantageously used as light absorbents sensitive to laser beams withwavelengths around 650 nm in high density optical recording media suchas DVD-Rs.

[0023] The cyanine dyes of the present invention for use in the opticalrecording media according to the present invention can be prepared inaccordance with the preparation methods for conventional opticalrecording media because the cyanine dyes do not require any specialtreatment and handling when used in optical recording media. Forexample, to control the reflectance and the absorptance in recordinglayers, one or more of the cyanine dyes of the present invention aslight absorbents can be, if necessary, incorporated with one or moreother organic dye compounds sensitive to visible light and further, toimprove the processibility and ability of the optical recording media,one or more conventionally used light resistant improvers, binders,dispersants, flame retardants, lubricants, antistatic agents,surfactants, and plasticizers. The resulting mixtures are then dissolvedin organic solvents, and the solutions are homogeneously coated overeither surface of substrates by spraying, soaking, roller coating, orrotary coating method; and dried to form thin layers as recording layersmade of light absorbents and, if necessary, followed by formingreflection layers to be closely attached on the recording layers bymeans of vacuum deposition, chemical vapor deposition, sputtering, orion-planting method using metals such as gold, silver, copper, platinum,aluminum, cobalt, tin, nickel, iron, and chromium or using commonly usedmaterials for organic reflection layers to attain a reflectionefficiency of 45% or higher, preferably, 55% or higher. Alternatively,to protect the recording layers from scratches, dust, stains, etc.,coatings may be applied over the recording layers with ultraviolet rayhardening resins or thermosetting resins which contain flame retardants,stabilizers, or antistatic agents, and then the coatings are hardened byirradiating light or heating to form protective layers attached closelyover the reflection layers. Thereafter, if necessary, a pair of theabove substrates with recording-, reflection-, and protecting-layers areplaced while facing the protective layers each other and attachedtogether using, for example, adhesives or viscous sheets; or protectiveplates, which are made of similar materials and shapes as in thesubstrates, are attached to the protective layers.

[0024] Other organic dye compounds used in combination with the cyaninedyes of the present invention are not specifically restricted as long asthey are sensitive to visible light and capable of controlling thereflectance or the absorptance of recording layers of optical recordingmedia when used in combination with the cyanine dyes. Examples of suchorganic dye compounds are polymethine dyes such as styryl, merocyanine,oxonol, azulenium, squallilium, pyrylium, thiopyrylium, and phenanthrenedyes, which have either a monomethine chain that may have one or moresubstituents or a polymethine chain such as di-, tri-, tetra-, penta-,hexa-, and hepta-methine-chains, wherein the both ends of themonomethine chain or the polymethine chain bind the same or differentcyclic cores such as imidazoline, imidazole, benzimidazole,α-naphthoimidazole, β-naphthoimidazole, indole, isoindole, indolenine,isoindolenine, benzindolenine, pyridinoindolenine, oxazoline, oxazole,isoxazole, benzoxazole, pyridineoxazole, α-naphthoxazole,β-naphthoxazole, selenazoline, selenazole, benzoselenazole,α-naphthoselenazole, β-naphthoselenazole, thiazoline, thiazole,isothiazole, benzothiazole, α-naphthothiazole, β-naphthothiazole,tellulazoline, tellulazole, benzotellulazole, β-naphthotellulazole,β-naphthotellulazole, aquaridine, anthracene, isoquinoline, isopyrrole,imidaquinoxaline, indandione, indazole, indazoline, oxadiazole,carbazole, xanthene, quinazoline, quinoxaline, quinoline, chroman,cyclohexanedione, cyclopentanedione, cinnoline, thiodiazole,thiooxazolidone, thiophene, thionaphthene, thiobarbitur, thiohydantoin,tetrazole, triazine, naphthalene, naphthyridine, piperazine, pyrazine,pyrazole, pyrazoline, pyrozolone, pyran, pyridine, pyridazine,pyrimidine, pyrylium, pyrrolidine, pyrroline, pyrrole, phenazine,phenanthridine, phenanthrene, phenanthroline, phthalazine, pteridine,furazan, furan, purine, benzene, benzoxazine, benzopyran, morpholine,and rhodanine rings,which may have one or more substituents. Inaddition, the following organic dye compounds can be exemplified;acridine, thioindigo, tetrapyraporphyradine, triphenylmethine,triphenylthiazine, napthoquinone, phthalocyanine, benzoquinone,benzopyran, benzofuranone, porphyrin, rhodamine dyes, and their relatedcompounds. Depending on use, the above organic dye compounds can be usedin an appropriate combination. Preferable organic dye compounds used incombination with the cyanine dyes of the present invention are thosewhich have absorption maxima in a visible region, particularly, those atwavelengths of 400-850 nm, when in a thin layer form.

[0025] The light-resistant improvers used in the present invention are,for example, nitroso compounds such as nitrosodiphenylamine,nitrosoaniline, nitrosophenol, and nitrosonaphthol; and metal complexessuch as tetracyanoquinodimethane compounds, diimmonium salts, “NKX-1199”(bis[2′-chloro-3-methoxy-4-(2-methoxyethoxy)dithiobenzyl]nickel)produced by Hayashibara Biochemical Laboratories, Inc., Okayama, Japan,azo dye metal complexes, and formazan complexes, which all can be usedin an appropriate combination, if necessary. Preferable light resistantimprovers are those which contain nitroso compounds or formazan metalcomplexes; nitroso compounds having a phenylpyridylamine skeleton asdisclosed in Japanese Patent Application No. 88,983/99, titled“Phenylpyridylamine derivatives” applied for by the same applicant asthe present invention, and those which contain metal complexes composedof metals such as nickel, zinc, cobalt, iron, copper, palladium, etc.,and, as ligands, one or more of the formazan compounds and theirtautomers, which have a pyridine ring at C-5 of the formazan skeletonand have a pyridine or furan ring bound to C-3 of the formazan skeletonas disclosed in Japanese Patent Application No. 163,036/99, titled“Formazane metal complex” applied for by the same applicant as thepresent invention. The combination use of the light resistant improversand the cyanine dyes of the present invention effectively inhibits theundesirable deterioration, fading, color change, and quality change ofthe cyanine dyes, which are inducible by the exposure of reading andenvironmental light, without lowering the solubility of the cyanine dyesin organic solvents and substantially spoiling their preferable opticalproperties. As for the composition ratio, 0.01-5 moles, preferably,0.1-1 mole of a light resistant improver(s) can be incorporated into onemole of the present cyanine dye(s) while increasing or decreasing theratio.

[0026] The light resistant improvers should not necessarily existseparatory from the cyanine dyes of the present invention and, ifnecessary, the cyanine dyes can be formulated into salts, complexes, orcompounds by combining with commonly used organic metal complex anions,which are capable of improving the light resistance, such as those ofazo, bisphenyldithiol, phenylbisdiol, thiocatecholchelate,thiobisphenolatechelate, or bisdithiol-α-diketone, by using appropriatespacers and crosslinking agents, for example, alkoxides or cyanates ofmetal elements such as titanium, zirconium, and aluminum; or usingcomplexes of these metal elements having carbonyl compounds or hydroxycompounds as ligands. Azo organic metal complex anions are preferablyused in the present invention and examples of which are thoserepresented by Formulae 6 to 10.

[0027] Throughout Formulae 6 to 9, R₄ to R₇ independently denotehydrogen atoms; halogens such as fluorine, chlorine, bromine, andiodine; aliphatic hydrocarbons such as methyl, trifluoromethyl, ethyl,propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, pentyl, isopentyl,neopentyl, tert-pentyl, hexyl, and isohexyl groups; ether groups such asmethoxy, trifluoromethoxy, ethoxy, propoxy, isopropoxy, butoxy, andtert-butoxy groups; ester groups such as methoxycarbonyl,phenoxycarbonyl, acetoxy, trifluoroacetoxy, and benzoyloxy groups;alkylaminosulfonyl groups such as methylaminosulfonyl,dimethylaminosulfonyl, ethylaminosulfonyl, diethylaminosulfonyl,propylaminosulfonyl, and isopropylaminosulfonyl; or others such as cyanoand nitro groups. Y and Y′ are, for example, the same or differenthetero atoms selected from the 16 group in the periodic table such asoxygen, sulfur, selenium, and tellurium. In Formulae 6 to 10, M is acentral metal and is generally, for example, one selected from metalelements from the 3-12 groups in the periodic table such as scandium,yttrium, titanium, zirconium, vanadium, niobium, chrome, molybdenum,manganese, technetium, iron, rubidium, cobalt, rhenium, nickel,palladium, copper, silver, zinc, and cadmium.

[0028] Throughout Formula 6 and Formulae 7 to 10, R₈ and R₉ eachindependently denotes a hydrogen atom or, for example, a halogen such asfluorine, chlorine, bromine, or iodine; an aliphatic hydrocarbon groupsuch as methyl, ethyl, propyl, isopropyl, butyl, or tert-butyl group; anether group such as methoxy, trifluoromethoxy, ethoxy, propoxy,isopropoxy, butoxy or tert-butoxy group; a substituted or unsubstitutedaliphatic, alicyclic or aromatic amino group, for example, amonomethylamino, dimethylamino, monoethylamino, diethylamino,monopropylamino, dipropylamino, monoisopropylamino, diisopropylamino,monobutylamino, dibutylamino, anilino, o-toluidino, m-toluidino,p-toluidino, xylidino, pyridylamino, piperidinyl, piperidino, orpyrrolidino group; or a hydroxy, carboxy, carbamoyl, sulfo, orsulfonamide group. One or more of the hydrogen atoms of thesesubstituted amino, carbamoyl, sulfo, and sulfonamide groups may bereplaced with halogens such as fluorine, chlorine, bromine, and iodine;aliphatic hydrocarbons such as methyl, ethyl, propyl, and butyl groups;ethers such as methoxy, trifluoromethoxy, ethoxy, and propoxy groups;aromatic hydrocarbon groups such as phenyl, biphenyl, o-tolyl, m-tolyl,p-tolyl, o-cumenyl, m-cumenyl, p-cumenyl, xylyl, and mesityl groups; orother substituents such as carboxy, hydroxy, cyano, and nitro groups.

[0029] Throughout Formulae 8 and 10, R₁₀ to R₁₃ each independentlydenotes a hydrogen atom or other groups, for example, aliphatichydrocarbons such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl,sec-butyl, tert-butyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,pentyl, isopentyl, neopentyl, and tert-pentyl groups. These aliphatichydrocarbons may contain one or more substituents, and examples of suchsubstituents are halogens such as fluorine, chlorine, bromine, andiodine; ethers such as methoxy, trifluoromethoxy, ethoxy, propoxy,isopropoxy, butoxy, and tert-butoxy groups; aromatic hydrocarbon groupssuch as phenyl, biphenyl, o-tolyl, m-tolyl, p-tolyl, o-cumenyl,m-cumenyl, p-cumenyl, xylyl, mesityl, and naphthyl groups; and otherssuch as carboxy, hydroxy, cyano, and nitro groups.

[0030] In Formula 9, A and A′ are the same or different heterocyclicgroups with a five to ten membered ring structure, for example, furyl,thienyl, pyrolyl, pyridyl, piperidinio, piperydil, quinolyl, isoxazolyl,thiazolynyl, and imidazolynyl groups, which contain one or more heteroatoms selected from nitrogen, oxygen, sulfur, selenium, and telluriumatoms. Examples of the heterocyclic groups may contain one or moresubstituents, for example, aliphatic hydrocarbons such as methyl,trifluoromethyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,tert-butyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, pentyl,isopentyl, neopentyl, and tert-pentyl groups; esters such asmethoxycarbonyl, trifluoromethoxy, ethoxycarbonyl, acetoxy,trifluoroacetoxy, and benzoyloxy groups; aromatic hydrocarbon groupssuch as phenyl, biphenyl, o-tolyl, m-tolyl, p-tolyl, o-cumenyl,m-cumenyl, p-cumenyl, xylyl, mesityl, and naphthyl groups; and otherssuch as cyano and nitro groups.

[0031] All the above-mentioned organic metal complex anions includingazo metal complexes can be prepared by conventional methods or inaccordance therewith. The cyanine dyes of the present invention, whichcomprise the above anions as counter ions, have in themselves lightresistance and do not necessary require the combination use of otherlight resistant improvers as essential elements when used in highdensity optical recording media such as DVD-Rs. As a result, the cyaninedyes of the present invention can be freely coated on substrates foroptical recording media without considering their solubility with lightresistant improvers when in the form of a liquid or amorphous. Based onthe same reason, the cyanine dyes of the present invention can beadvantageously used not only as light absorbents for forming pits onsubstrates but as materials for improving light resistance of otherlight absorbents. Examples of the cyanine dyes of the present invention,which have organic metal complex ions as counter ions, include thoserepresented by Chemical Formulae 3, 6, 14, 16, 25 and 27.

[0032] The cyanine dyes of the present invention have satisfactorysolubility in organic solvents without substantially causing no actualproblem and dot not substantially restrict organic solvents used forcoating the cyanine dyes onto substrates. Thus, in the preparation ofoptical recording media according to the present invention, for example,TFP used frequently to prepare optical recording media and the followingorganic solvents other than TFP can be selected and appropriately usedin combination: For example, hydrocarbons such as hexane, cyclohexane,methylcyclohexane, dimethylcyclohexane, ethylcyclohexane,isopropylcyclohexane, tert-butylcyclohexane, octane, cyclooctane,benzene, toluene, and xylene; halogen compounds such as carbontetrachloride, chloroform, 1,2-dichloroethane, 1,2-dibromoethane,trichloroethylene, tetrachloroethylene, chlorobenzene, bromobenzene, andα-dichlorobenzene; alcohols and phenols such as methanol, ethanol, 22,2-trifluoroethanol, 1-propanol, 2-propanol, 1-methoxy-2-propanol,1-ethoxy-2-propanol, 1-butanol, 1-methoxy-2-butanol,3-methoxy-1-butanol, 4-methoxy-1-butanol, isobutyl alcohol, pentylalcohol, isopentyl alcohol, cyclohexanol, 2-methoxyethanol (methylcellosolve), 2-ethoxyethanol (ethyl cellosolve), 2-propoxy-1-ethanol,diethylene glycol, triethylene glycol, propylene glycol, glycerine,phenol, benzyl alcohol, cresol, and diacetone alcohol; ethers such asdiethyl ether, diisopropyl ether, tetrahydrofuran, tetrahydropyran,1,4-dioxane, anisole, 1,2-dimethoxyethane, diethylene glycol dimethylether, dicyclohexyl-18-crown-6, methyl carbinol, and ethylcarbitol;ketones such as furfural, acetone, ethyl methyl ketone, andcyclohexanone; esters such as ethyl acetate, butyl acetate, ethylenecarbonate, propylene carbonate, and trimethyl phosphate; amides such asformamide, N-methyl formamide, N,N-dimethylformamide, andhexamethylphosphoric triamide; nitrites such as acetonitrile,propionitrile, and succinonitrile; nitro compounds such as nitromethaneand nitrobenzene; amines such as ethylene diamine, pyridine, piperidine,morpholine, and N-methylpyrrolidone; and sulfur atom-containingcompounds such as dimethylsulfoxide and sulfolane.

[0033] Particularly, since the cyanine dyes of the present inventionhave relatively high solubility in easily volatile organic solvents suchas TFP, diacetone alcohol, methyl cellosolve, and ethyl cellosolve, theyare substantially free from dye crystallization and inconsistency of themembrane thickness and the surface of recording layers when they aredissolved in the organic solvents, coated on substrates, and then dried;and are free of causing inconsistency of thickness and surface of theformed recording layers. The cyanine dyes of the present invention havealso satisfactory solubility in non-halogen solvents, for example,alcohols such as methyl cellosolve, ethyl cellosolve, and diacetonealcohol; and ketones such as cyclohexanone. As the merit, the abovealcohols scarcely damage the substrates or spoil the environment whenused to dissolve the cyanine dyes of the present invention for coatingonto the substrates.

[0034] Commercialized substrates can be used in the present invention,and usually the substrates used in the present invention can beprocessed with appropriate materials, for example, into discs, 12 cm indiameter and 0.6 mm or 1.2 mm in thickness, to fulfill the final use bythe methods such as compression molding, injection molding,compression-injection molding, photopolymerization method (2P method),thermosetting integral method, and lightsetting integral method. Thediscs thus obtained can be used singularly or plurally afterappropriately attaching them together with adhesives, adhesive sheets,etc. In principal, any materials for the substrates can be used in thepresent invention as long as they are substantially transparent and havea transmittance of at least 80%, preferably, at least 90% at awavelength ranging from 400 nm to 800 nm. Examples of such materials areglasses, ceramics, and others such as plastics including polyacrylate,poly(methyl methacrylate), polycarbonate, polycarbonate, polystyrene(styrene copolymer), polymethylpentene, polyester, polyolefin,polyimide, polyetherimide, polysulfone, polyethersulfone, polyarylate,polycarbonate/polystyrene alloy, polyestercarbonate,polyphthalatecarbonate, polycarbonateacrylate, non-crystallinepolyolefin, methacrylate copolymer, diallylcarbonatediethylene-glycol,epoxy resin, and phenol resin, among which polycarbonate is frequentlyused. In the case of plastic substrates, concaves for expressingsynchronizing-signals and addresses of tracks and sectors are usuallytransferred to the internal circuit of the tracks during theirformation. The form of concaves are not specifically restricted andpreferably formed to give 0.3-0.8 μm in average wide and 70-200 nm inwidth.

[0035] Considering the viscosity, the light absorbents of the presentinvention are prepared into 0.5-5% (w/w) solutions in the above organicsolvents, and then uniformly coated over the substrates to form a driedrecording layer of 10-1,000 nm, and preferably 50-300 nm in thickness.Prior to the coating of the solutions, preliminary layers can be formedover the substrates to protect the substrates and improve the adhesionability of the substrates, if necessary. Materials for the preliminarylayers are, for example, high molecular substances such as ionomerresins, polyamide resins, vinyl resins, natural resins, silicon, andliquid rubbers. In the case of using binders, the following polymers canbe used alone or in combination in a weight ratio of 0.01-10 times ofthe cyanine dye(s): Cellulose esters such as nitrocellulose, cellulosephosphate, cellulose sulfate, cellulose acetate, cellulose propionate,cellulose lactate, cellulose palmitate, and celluloseacetate/propionate; cellulose ethers such as methyl cellulose, ethylcellulose, propyl cellulose, and butyl cellulose; vinyl resins such aspolystyrene, poly(vinyl chloride), poly(vinyl acetate), poly(vinylacetal), poly(vinyl butyral), poly(vinyl formal), poly(vinyl alcohol),and poly(vinyl pyrrolidone); copolymer resins such as styrene-butadienecopolymers, styrene-acrylonitrile copolymers,styrene-butadiene-acrylonitrile copolymers, vinyl chloride-vinyl acetatecopolymers, and maleic anhydride copolymers; acrylic resins such aspoly(methyl methacrylate), poly(methyl acrylate), polyacrylate,polymethacrylate, polyacrylamide, and polyacrylonitrile; polyesters suchas poly(ethylene terephthalate); and polyolefins such as polyethylene,chlorinated polyethylene, and polypropylene.

[0036] Explaining the method for using the optical recording mediaaccording to the present invention, the high density optical recordingmedia such as DVD-Rs according to the present invention can writeinformation at a relatively high density by using laser beams withwavelengths around 650 nm, particularly, 635-660 nm irradiated bysemiconductor lasers such as those of AlGaInP, GaAsP, GaAlAs, InGaP,InGaAsP, and InGaAlP; or YAG lasers combined with second harmonicgeneration inducing elements (SHG elements). To read information, laserbeams are used which have wavelengths identical to or slightly longerthan those used for writing information. As for the laser power forwriting and reading information, in the optical recording media of thepresent invention, it is preferably set to a relatively high level whichexceeds the threshold of the energy required for forming pits when usedfor writing information, while it is preferably set to a relatively lowlevel, i.e., a level below the threshold, when used for reading therecorded information, although the power levels vary depending on thetypes and ratios of other organic dye compounds and light resistantimprovers which are used in combination with the cyanine dyes of thepresent invention: Generally, the power levels can be controlled topowers of at least 5 mW, usually, 10-50 mW for writing; and to powers ofnot higher than 5 mW, usually, 0.1-5 mW for reading. The recordedinformation is read out by detecting the change of the reflection lightlevel or the transmission light level in the pits and the pit-less partson the recorded surface of optical recording media.

[0037] Accordingly, in the optical recording media according to thepresent invention, minute pits, having a pit width of below 0.834 μm/pitat a track pitch of below 1.6 μm used commonly in the standard CD-R, canbe formed stably at a relatively high density by using a light pickup ofa laser beam with a wavelength around 650 nm, particularly, 635-660 nm.For example, in the case of using a substrate, 12 cm in diameter, onecan prepare a high density optical recording medium having a recordingcapacity far exceeding 0.682 GB per one side and capable of recordinginformation in the form of images and sound for about two hours, whichthe capacity could not be easily attained by conventional cyanine dyes.

[0038] Since the optical recording media of the present invention canrecord information in the form of characters, images, sound, and otherdigital data at a relatively high density, they are advantageouslyuseful as recording media for professional and family use torecord/backup/keep documents, data, and computer softwares. Particularexamples of the kinds of industries and the forms of information, towhich the optical recording media of the present invention can beapplied, are as follows: Drawings of construction and engineering works,maps, ledgers of roads and rivers, aperture cards, architecturalsketches, documents of disaster protection, wiring diagrams, arrangementplans, information from newspapers and magazines, local information,reports of construction works, etc., which all relate to architectureand civil construction; blueprints, ingredient tables, prescriptions,product specifications, product price tables, parts lists, maintenanceinformation, case study files of accidents and problems, manuals forclaims, production schemes, technical documents, sketches, details,company house-made product files, technical reports, analysis reports,etc., which all relate to manufacturing; customer information,correspondent information, company information, contracts, informationfrom newspapers and magazines, business reports, reports of companycredibility, records of stocks, etc., which all relate to sales; acompany information, records of stocks, statistical documents,information from newspapers and magazines, contracts, customer lists,documents of application/notification/licenses/authorization, businessreports, etc., which all relate to finance; information regardingproperties, sketches of construction, maps, local information,information from newspapers and magazines, contracts of leases, companyinformation, stock lists, traffic information, correspondentinformation, etc., which all relate to real property andtransportations; diagrams of writings and piping arrangements, documentsof disaster protection, tables of operation manuals, documents ofinvestigations, technical reports, etc., which all relate to electricand gas supplies; patient files, files of patient clinical histories andcase studies, diagrams of medical care/institution relationships, etc.,which all relate to medical fields; texts, collections of questions,educational documents, statistical information, etc., which all relateto private and preparatory schools; scientific papers, records inacademic societies, monthly reports of research, research data,documentary records and indexes thereof, etc., which all relate touniversities, colleges, and research institutes; inspection data,literatures, patent publications, weather maps, analytical records ofdata, customer files, etc., which all relate to information; casestudies on laws; membership lists, history notes, records ofworks/products, competition data, data of meetings/congresses, etc.,which all relate to organizations/associations; sightseeing information,traffic information, etc., which all relate to sightseeing; indexes ofhomemade publications, information from newspapers and magazines, who'swho files, sport records, telop files, scripts for broadcastings, etc.,which all relate to mass communication and publishing; and maps, ledgersof roads and rivers, fingerprint files, resident cards, documents ofapplication/notification/license/authorization, statistical documents,public documents, etc., which all relate to government offices.Particularly, the write-once type optical recording media of the presentinvention can be advantageously useful for storing records of patientfiles and official documents, which must not be deleted or rewrittenintentionally, and also used as electronic libraries for art galleries,libraries, museums, broadcasting stations, etc.

[0039] As a rather specific use, the optical recording media of thepresent invention can be used to prepare and edit compact discs, digitalvideo discs, laser discs, MDs (a mini disc as information recordingsystem using photomagnetic disc), CDVs (a laser disc using compactdisc), DATs (an information recording system using magnetic tape),CD-ROMs (a read-only memory using compact disc), DVD-ROMs (a read-onlymemory using digital video disc), DVD-RAMs (a writable and readablememory using digital video disc), digital photos, movies, videosoftware, audio software, computer graphics, publishing products,broadcasting programs, commercial messages, game software, etc.; andused as external program recording means for large-sized computers andcar navigation systems.

[0040] Hereinbefore, the use of the cyanine dyes of the presentinvention in the field of optical recording media has been mainlylimited to high density optical recording media which use laser beamswith wavelengths around 650 nm as a writing light. However, in the fieldof optical recording media, the cyanine dyes of the present inventioncan be advantageously used not only in high density optical recordingmedia such as DVD-Rs but in commonly used optical recording media suchas CD-Rs as materials for controlling and calibrating the absorptanceand the reflectance, for example, by combining them with one or moreother organic dye compounds sensitive to laser beams with wavelengths of775-795 nm. Even in the case of applying to high density opticalrecording media which use laser beams with wavelengths around 650 nm asa writing light, pits can be indirectly formed, without directly formingpits on substrates using the cyanine dyes of the present invention, bycombining with one or more other organic dye compounds sensitive to alonger wavelength light, for example, laser beams with wavelengths of775-795 nm, in such a manner that an exited energy induced by laserbeams with wavelengths around 650 nm is transferred through the cyaninedyes of the present invention to the organic dye compounds to decomposethe compounds. The term “optical recording media” as referred to in thepresent invention means those in general which use the characteristicfeatures of specific cyanine dyes that substantially absorb visiblelight with wavelengths around 650 nm, and includes, in addition toorganic ablation-type optical recording media, for example, thoseprepared by the thermal coloration method which uses the chemicalreaction between coloring agents and developers induced by the heatgenerated when the organic dye compounds absorb light, and thoseprepared by the technique called “moth-eye type technique” which usesthe phenomenon that the above heat smoothes the pattern of periodicalunevenness, provided on the surface of substrates.

[0041] The cyanine dyes of the present invention substantially absorbvisible light with wavelengths around 650 nm, and therefore in additionto the use in the aforesaid optical recording media, the lightabsorbents comprising the cyanine dyes can be advantageously used asmaterials for polymerizing polymerizable compounds by exposure tovisible light, sensitizing solar batteries, laser action substances indye lasers, and dyeing clothes. If necessary, in combination with one ormore other light absorbents capable of absorbing light in ultraviolet-,visible- and/or infrared-regions, the light absorbents of the presentinvention can be used in clothes in general and other materialsincluding building/bedding/decorating products such as drapes, laces,casements, prints, venetian blinds, roll screens, shutters, shopcurtains, blankets, thick bedquilts including comforters, peripheralmaterials for thick bedquilts, covers for thick bedquilts, cottons forthick bedquilts, bed sheets, Japanese cushions, pillows, pillow covers,cushions, mats, carpets, sleeping bags, tents, interior finishes forcars, and window glasses including car window glasses; sanitary andhealth goods such as paper diapers, diaper covers, eyeglasses, monocles,and lorgnettes; internal base sheets/linings/materials for shoes;wrappers; materials for umbrellas; parasols; stuffed toys; lightingdevices; filters/panels/screens for information displaying devices suchas televisions and personal computers which use cathode-ray tubes,liquid crystal displays, electroluminescent displays, and plasmadisplays; sunglasses; sunroofs; sun visors; PET (polyethyleneterephthalate) bottles; storage; vinyl houses; lawns; optical fibers;prepaid cards; and windows of ovens including electric ovens. When usedfor wrapping, injecting, and enclosing the above articles, the lightabsorbents of the present invention advantageously prevent living bodiesand products from problems and discomforts induced by environmentallight such as natural and artificial light or minimize the aboveproblems and discomforts, and they can advantageously regulate thecolor, tint, and appearance and adjust the light reflected from orpassed through the articles to a desired color balance.

[0042] The following examples describe the preferred embodimentsaccording to the present invention:

EXAMPLE 1 Cyanine Dyes

[0043] To a vessel were added 20 ml of acetonitrile and further added10.0 g of1-butyl-3,3-dimethyl-2-[(phenylamino)ethenyl]benzoindolium=p-toluenesulfonate,7.6 g of 1,3-dimethyl-2-methylimidazoquinoxalium=p-toluenesulfonate, andtwo milliliters of acetic anhydride. Under stirring conditions atambient temperature, to the mixture was dropped six milliliters oftriethylamine, followed by stirring for two hours. The resulting crudecrystals were filtered and dissolved by stirring in an adequate amountof methanol, followed by filtering the resulting solution. The filtratethus obtained was admixed with an aqueous solution containing 3.0 g ofsodium perchlorate, and the mixture was stirred for 30 min to effect ionexchange. Thereafter, the formed crystals were filtered, washed withmethanol, and dried to obtain eight grams of a black crystal of thecyanine dye represented by Chemical Formula 10.

[0044] A portion of the black crystal was measured for melting point andrevealed that it had a melting point of 301-302° C.

[0045] Although the production conditions and yields are varied to someextent depending on the structure of the cyanine dyes of the presentinvention, all the cyanine dyes including those represented by Formulae1 to 27 can be yielded in a desired amount by the method in Example 1 orin accordance therewith.

EXAMPLE 2 Optical Property of Cyanine Dye

[0046] The cyanine dyes in Table 1 were measured in a usual manner forvisible absorption spectra in such a manner of dissolving them inmethanol or allowing them to form layers on glass substrates todetermine their absorption maxima when in solution and thin layer forms,respectively. The results are in Table 1. FIGS. 1 and 2 are visibleabsorption spectra for the cyanine dyes represented by Chemical Formulae12 and 23, respectively. TABLE 1 Wavelength of Melting Decompositionabsorption maximum (nm) point point Solubility Cyanine dye Solution Thinlayer (° C.) (° C.) (mg/ml) Chemical Formula 4 583 632 — 324.3 4.9Chemical Formula 5 583 593 249.1 274.9 158.5 Chemical Formula 6 582 614— 313.0 70.0 Chemical Formula 12 586 631 — 307.4 69.5 Chemical Formula16 588 600 252.1 292.8 93.2 Chemical Formula 23 584 638 — 308.0 16.3Chemical Formula 24 592 653 — 292.0 9.1 Chemical Formula 25 584 630 —312.8 26.6 Chemical Formula 27 592 637 — 298.5 68.3

[0047] As evident from the results in Table 1, the cyanine dyes testedaccording to the present invention had absorption maxima at wavelengthsaround 580 nm when in a solution form and at wavelengths around 630 nmwhen in a thin layer form. As evident from the visible absorptionspectra in FIGS. 1 and 2, the absorption ends at the longer wavelengthof the cyanine dyes of the present invention extended up to a wavelength around 700 nm. These results indicate that the cyanine dyes ofthe present invention have absorption maxima in a visible region andsubstantially absorb visible light with wavelengths around 650 nm whenin a thin layer form.

EXAMPLE 3 Thermal Property of Cyanine Dye

[0048] As a test specimen, an adequate amount of any one of the cyaninedyes in Table 1 was provided and subjected to conventional differentialthermal analysis (hereinafter abbreviated as “DTA”) andthermogravimetric analysis (hereinafter abbreviated as “TGA”) using“MODEL TG/DTA 220”, a digital thermo analyzer commercialized by SeikoInstruments Inc., Tokyo, Japan, to determine the decomposition point.The results are in Table 1. FIGS. 3 and 4 are respectively the resultson DTA and TGA of the cyanine dyes of the present invention, representedby Chemical Formulae 12 and 23. In the TGA and DTA, the environmentaltemperature was set to an increasing temperature mode at a rate of 10°C./min.

[0049] As evident from the results in Table 1 and FIGS. 3 and 4, thecyanine dyes of the present invention have a decomposition point of over270° C., preferably, 300° C. or higher, and have a relatively highthermal property. Most of the cyanine dyes tested had only decompositionpoints or decomposition points undistinguishable from their meltingpoints, and promptly decomposed at around their decomposition points. Asdescribed above, when used in high density optical recording media suchas DVD-Rs, loosely-decomposing organic dye compounds are difficult forforming minute pits on a restricted recording surface at a relativelyhigh density. Varying depending on the glass transition temperature ofsubstrates, when used as a light absorbent in optical recording media,dyes with lower decomposition points can be generally used to writeinformation using relatively low power laser beams as an advantage,however, as a disadvantage, when exposed to laser beams for a relativelylong period of time on reading, optical recording media processed withsuch dyes may easily accumulate heat and deform parts around pits andpit-less parts on recording surfaces, resulting in undesirable jittersand reading errors. Most of the cyanine dyes of the present inventionhave only relatively high decomposition points or decomposition pointsundistinguishable from their melting points, and promptly decompose attheir decomposition points. These characteristic features indicate thathigh density optical recording media, which have a relatively smalljitter, insubstantial reading error, and satisfactory stability againstexposure to environmental light such as reading and natural light, canbe obtained by using the cyanine dyes of the present invention as lightabsorbents.

EXAMPLE 4 Optical Recording Media

[0050] Either of the cyanine dyes, represented by Chemical Formulae 12and 23, as light absorbents, was added to TFP to give a concentration of2.0% (w/w), and further admixed with, as a light resistant improver, theformazan metal complex represented by Chemical Formula 28, where thesolid line drawn between the nickel atom and the nitrogen atom means acovalent bond and the dotted line means a coordinate bond, to give aconcentration of 0.2% (w/w), followed by heating and ultrasonicallydissolving the contents. According to a usual manner, the resultingsolution was filtered with a membrane, and the filtrate washomogeneously coated on either surface of a polycarbonate discsubstrate, 12 cm in diameter and 0.6 mm in thickness, which concaves,0.74 μm in track pitch, 0.03 μm in wide, and 76 nm in width, forexpressing synchronizing-signals and addresses of tracks and sectors hadbeen transferred to the track's internal circuit, and dried to form arecording layer, 100 nm in thickness. Thereafter, the resultingsubstrate was deposited with gold to form a reflection layer, 100 nm inthickness, to be attached closely on the surface of the recording layer,and the reflection layer was homogeneously coated in a rotary mannerwith “DAICURE CLEAR SD1700”, a known ultraviolet ray hardening resincommercialized by Dainippon Ink and Chemicals, Inc., Tokyo, Japan, andirradiated to form a protection layer to be attached closely on thesurface of the reflection layer, followed by closely attaching on theprotection layer a polycarbonate disc as a protection substrate, 12 cmin diameter and 0.6 mm in thickness, to obtain different types ofoptical recording media.

[0051] Chemical Formula 28:

[0052] The optical recording media thus obtained have a recordingcapacity of over 4 GB and can record a large amount of information inthe form of documents, images, sound, and other digital data at arelatively high density by using laser elements with an oscillationwavelength around 650 nm. Electron microscopic observation of therecorded surface of the optical recording media of this example, whichhad been written information by using a semiconductor laser element withan oscillation wavelength of 658 nm, revealed the formation of minutepits below 1 μm/pit at a track pitch of below 1 μm and at a relativelyhigh density.

INDUSTRIAL APPLICABILITY

[0053] As described above, the present invention was made based on thecreation of novel trimethine cyanine dyes and their industrially usefulproperties. The cyanine dyes of the present invention have absorptionmaxima in a visible region and substantially absorb visible light withwavelengths around 650 nm when in a thin layer form, and have relativelyhigh decomposition points and thermal resistance. Based on theseproperties, the cyanine dyes of the present invention have diversifieduses in the fields of optical recording media, photochemicalpolymerization, solar batteries, dyeing, etc., which require organic dyecompounds having the above properties, particularly, in the field ofoptical recording media, the cyanine dyes are outstandingly useful aslight absorbents in high density optical recording media in which minutepits must be stably and promptly formed on a restricted recordingsurface at a relatively high density when in writing information, forexample, when used particularly in DVD-Rs using laser beams withwavelengths of around 650 nm as a writing light.

[0054] As compared with the CD-Rs now used, the organic opticalrecording media of the present invention, which use the aforesaid lightabsorbents and write information using laser beams with wavelengthsaround 650 nm, can stably and promptly form minute pits at a relativelynarrower track pitch and a relatively high density, and can record avast amount of information in the form of characters, images, sound, andother digital data at a relatively high density, resulting in greatlylowering the cost for recording information per bit as a merit.

[0055] The cyanine dyes with such usefulness can be easily obtained in adesired amount by the process of the present invention which compriseseither reacting a benzoindolium compound having a compatible leavinggroup with a pyrazinoimidazolium compound having a reactive methylgroup; or reacting a benzoindolium compound having a reactive methylgroup with a pyrazinoimidazolium compound having a compatible leavinggroup.

[0056] The present invention having these outstanding effects andfunctions is a significant invention that will greatly contribute tothis art.

1. A trimethine cyanine dye represented by Formulae 1:

wherein in Formula 1, R₁, R₂ and R₃ are the same or different aliphatichydrocarbon groups which are optionally substituted; Z₁ and Z₂ eachrepresents a condensed naphthalene ring or a condensed quinoxaline ringfor forming a benzoindolenine ring and a pyrazinoimidazole ring,respectively; and X⁻ represents a compatible counter-ion.
 2. Thetrimethine cyanine dye of claim 1, wherein X⁻ is an organic metalcomplex anion.
 3. The trimethine cyanine dye of claim 1 or 2, wherein X⁻is an azo metal complex anion.
 4. The trimethine cyanine dye of claim 1,2 or 3, which substantially absorbs a visible light with a wavelength ofaround 650 nm.
 5. The trimethine cyanine dye of any one of claims 1 to4, which has only a decomposition point or a decomposition pointundistinguishable from its melting point, said decomposition point beingover 280° C.
 6. A light absorbent comprising the trimethine cyanine dyeof any one of claims 1 to
 5. 7. The light absorbent of claim 6, whichcomprises the trimethine cyanine dye of any one of claims 1 to 5 and oneor more other organic dye compounds sensitive to a visible light.
 8. Thelight absorbent of claim 6 or 7, which comprises the trimethine cyaninedye of any one of claims 1 to 5 and one or more compatible lightresistant improvers.
 9. The light absorbent of claim 6, 7 or 8, which issensitive to a laser beam with a wavelength around 650 nm when in a thinlayer form.
 10. An optical recording medium comprising the dimethinecyanine dye of any one of claims 1 to
 5. 11. The optical recordingmedium of claim 10, which has a recording layer comprising thetrimethine cyanine dye of any one of claims 1 to 5 and one or more otherorganic dye compounds sensitive to a visible light.
 12. The opticalrecording medium of claim 10 or 11, which has a recording layercomprising the trimethine cyanine dye of any one of claims 1 to 5 andone or more compatible light resistant improvers.
 13. The opticalrecording medium of claim 10, 11 or 12, which uses a laser beam with awavelength around 650 nm as a writing light.
 14. The optical recordingmedium of any one of claims 10 to 13, which is used as an organicablation-type optical recording medium.
 15. A process for producing thetrimethine cyanine dye of any one of claims 1 to 5, which comprises astep of reacting a compound, represented by Formula 2 having R₁ and Z₁corresponding to Formula 1, with a compound represented by Formula 3having R₂, R₃ and Z₂corresponding to Formula 1:

wherein in Fromulae 2 and 3, X₁ ⁻ and X₂ ⁻ denote compatiblecounter-ions, and L denotes a compatible leaving group.
 16. A processfor producing the trimethine cyanine dye of any one of claims 1 to 5,which comprises a step of reacting a compound, represented by Formula 4having R₁ and Z₁, corresponding to Formula 1, with a compoundrepresented by Formula 5 having R₂, R₃ and Z₂corresponding to Formula 1:

wherein in Formulae 4 and 5, X₁ ⁻ and X₂ ⁻ denote compatiblecounter-ions, and L denotes a compatible leaving group.